The Nova is a better speaker than the 801D, it produces a wider and slightly taller soundstage and the Beryillium tweeter is smoother than the B&W. I would say that at $40K the JM Labs are a bit pricey.
The B&W are very good at playing loud without distortion but I have never heard them sound great unless played by big solid state. The JM can work wonderfully with tube amplifiers.